This invention relates to insulated electrical coil assemblies for high temperature service typically finding use in solenoids, relays, and other electrical equipment requiring coils.
Presently, electrical coil assemblies are generally wound of insulated wire on a thermoplastic or thermoset bobbin. The wound coil is then varnish impregnated and wrapped with insulating tape. Space is left in the insulating tape for the exit of the coil leads. In the known techniques connecting terminals were then attached to the leads. A final wrap of tape is then required to position and secure the terminals. However, due to the nature of the assembly, the terminals were subject to damage from pull-out or other abuse encountered during handling and assembly.
Another prior art method employs wire wrapped about a plastic bobbin molded from a resilient thermoplastic material. The thermoplastic bobbin is contained in a housing formed from a similar thermoplastic material, when then relies upon a detent or snapin retaining method which is compatible with the resilient nature of the thermoplastic. An example of this latter type of assembly is described in U.S. Pat. No. 3,230,490. However, the relatively low temperature resisting properties of the thermoplastic family of materials as compared with the temperature resisting properties now available with the family of thermosetting plastics, prohibits the use of thermoplastic coil assemblies in high temperature environments.
A further prior art method employs "potting" the wound coil by pouring thermosetting resin around the coil as placed in a mold. This is a costly technique but heretofore has been the only thermoset encapsulation approach available since the temperatures and pressures encountered while injection molding a thermoset material around a coil caused damage to the winding insulation.
In view of the temperature limitations of thermoplastic material, the high cost of "potting" a wound coil with thermoset material, the high cost and inherent performance problems experienced with tape wound assemblies, plus the present inability of injection molding a thermoset material around a wound coil, a superior and more economical means of employing heat resisting thermoset materials has been sought.